Determination of the gas-phase decomposition rate constants of heptyl-1 and heptyl-2 hydroperoxides C7H15OOH

The gas-phase decomposition of n-heptyl-1 and n-heptyl-2 hydroperoxides C₇H₁₅OOH, which split into two radicals C₇H₁₅O and OH, has been investigated in the temperature range of 250–360°C. The decomposition has been carried out in a hydrogen–oxygen mixture (the hydroperoxide represents about 50 ppm) so as to avoid secondary reactions between the formed radicals and the reactants. Although the H₂–O₂ mixture is not spontaneously reactive in our conditions, it operates the transformation, through a fast and well-known process, of the OH radicals into HO₂ radicals and then into H₂O₂. However, C₇H₁₅O radicals are also transformed into HO₂ radicals and then into H₂O₂, but through an unknown process. To avoid heterogeneous reactions, vessel and probe are coated by B₂O₃ and then treated by the slow combustion of hydrogen at 510°C and 250 torr before the experiments are performed. As the reaction scheme is very simple, due to the use of the H₂–O₂ mixture, the determination of the evolutions of the HO₂ concentration (followed by electronic paramagnetic resonance) lead to the determination of the gas-phase decomposition rate constant of hydroperoxides. For the n-heptyl-1 hydroperoxide the rate constant is and for the n-heptyl-2 hydroperoxide it is .